Opiates are commonly abused substances, and forensic urine drug-testing for them involves an immunoassay screen and gas chromatographic/mass spectrometric (GC/MS) confirmation. There are also medical reasons to test urine for opiates, and confirmation procedures other than GC/MS are often used for medical drug-testing which are more compatible with the demands of clinical services and which identify a wider range of opiates than those in standard forensic batteries. One such procedure involves thin-layer chromatographic (TLC) analysis of opiate derivatives and can distinguish eight clinically encountered opiates, including morphine, acetylmorphine, hydromorphone, oxymorphone, codeine, dihydrocodeine, hydrocodone, and oxycodone. Medical drug-testing results are sometimes challenged by patients, causing physicians to request additional confirmation of the identified opiates. To our knowledge, no previous report examines all opiates specified above in a single GC/MS pr ocedure, but we find that they can be distinguished by GC/MS analyses of trimethylsilyl (TMS) ether derivatives, the mass spectra of which contain prominent molecular ions. Inclusion of deuterium-labeled internal standards permits quantitation of each of the eight opiates in urine. The GC/MS assay is linear over a concentration range which spans the TLC cutoff level, and coefficients of variation of 10% or less at concentrations below the TLC cutoff are achieved by for all opiates specified above except for oxymorphone and oxycodone, which exhibit coefficients of variation of 18-19%. This procedure has proved useful as a third-stage identification step for medical drug-testing specimens in which results from prior immunoassay and TLC analyses were challenged.